The present invention relates to gas spring suspension systems and more particularly to a gas spring suspension system that adjusts the spring rate as the travel is adjusted.
Bicycles include suspension systems to cushion the rider from irregularities in the terrain. Bicycle suspension systems are typically located at the front and rear forks, the seat tube, or at other bicycle frame locations. A typical front suspension fork includes two legs, each leg having inner and outer telescoping tubes. At least one leg includes a resilient member for biasing the inner and outer tubes apart from each other and for absorbing compressive forces applied to the fork. The resilient member may be a coil spring, an elastomer spring, a gas spring or the like. The maximum amount the tubes may compress relative to each other is commonly referred to as the travel of the fork. Early suspension forks were capable of about 50 mm of travel. However, as riders began to traverse rougher terrain at higher speeds, a greater amount of travel was needed to absorb the higher riding forces. Thus, newer suspension forks were designed with travel settings of 125 mm or more. However, forks with longer travel may be cumbersome to ride, especially when riding uphill, due to the raised front end geometry and the resulting softer spring rate. A rider may choose a fork according to the type of terrain he is going to be traversing. For example, a long travel fork is used for rough downhill terrain, a medium travel fork for flat terrain and a short travel fork for uphill terrain.
Another problem with existing bicycle suspension forks is that they are unnecessarily heavy. Besides increasing the overall weight of the bicycle, the weight of the fork affects the handling of the bicycle. Accordingly, reduced weight is important to riders, particularly to those involved in racing where reduced weight offers an important competitive advantage.
Bicycle suspension systems with adjustable travel have been designed, however, most use a helical compression spring that adds unnecessary weight. To solve this problem, gas spring suspension systems are sometimes used. One problem with existing gas spring forks is that the rider must perform a two-step process to adjust the travel. First, a knob is turned to select the desired travel, and then the fork is manually compressed to the desired travel setting. Therefore, there is a need for a lightweight bicycle suspension system that provides easily adjustable travel that can be optimized for downhill, flat and uphill terrain.